1. Field of the Invention
The present invention relates to a vehicle display device for displaying images by using optical reflection on a windshield (a glass window) disposed ahead of a vehicle driver.
2. Description of the Related Art
Common head-up display (HUD) devices for vehicles project display light including various kinds of information to be displayed as an image from an HUD unit onto a reflection board referred to as a front windshield or a combiner and form an optical path in such a manner that the light reflected on the front windshield and the like heads toward the viewpoint of a driver. The driver can visually recognize an image included in the display light emitted from the HUD unit and displayed on the front windshield and the like as a virtual image while visually recognizing the front view of the vehicle through the front windshield. The driver can visually recognize various kinds of information included in the display light emitted from the HUD unit while keeping usual driving conditions without moving the sightline.
With devices such as an HUD device that make various kinds of information included in display light visually recognized by using optical reflection on the surface of a windshield, the driver may visually recognize a distorted image. Optical reflection caused on the surface of an inclined windshield deforms the shape of the image. The gently curved surface shape of the windshield further distorts the image. The curvature and the inclination angle to the horizontal surface (or the vertical surface) are different between positions on the windshield, and the differences cause various kinds of distortion different depending on the positions where the display light is projected on the image visually recognized by the driver. Such distortion exert disadvantageous effects on the visually recognized image.
In this point of view, techniques for correcting distortion of an image in a vehicle HUD device have been developed (see Japanese Patent Application Laid-open No. 11-30764 and Japanese Patent Application Laid-open No. 2002-205571).
The display device of Japanese Patent Application Laid-open No. 11-30764 has a manual operation switch movable upward and downward. The device is configured such that an image is corrected with a manual operation of the switch. In such a case with a virtual image curved with its lateral dimension narrowing to the top or narrowing to the bottom, the image can be corrected by operating the switch.
The vehicle display device of Japanese Patent Application Laid-open No. 2002-205571 uses a coordinate conversion table for correcting distortion of a display image. The display device store the coordinate conversion table in a replaceable external read only memory (ROM) or non-volatile memory.
With the technique of Japanese Patent Application Laid-open No. 11-30764, distortion of an image resulting from the surface shape of the windshield or other factors can be corrected by operating the manual operation switch as necessary. With the technique of Japanese Patent Application Laid-open No. 2002-205571, distortion of a display image can be corrected by replacing the external ROM or rewriting the coordinate conversion table of the non-volatile memory.
However, the position of a viewpoint changes depending on the body size of a driver, the seat position, the posture of the driver, and other factors. The optical path, on which the display light heading toward the viewpoint travels, is accordingly changed. The change in the optical path changes the distortion level of the image.
With the technique of Japanese Patent Application Laid-open No. 11-30764, if a driver wants to visually recognize an image always in a distortion-free state, the driver needs to frequently operate the switch upon a change in the position of the viewpoint. With the technique of Japanese Patent Application Laid-open No. 2002-205571, it is necessary to replace the external ROM or rewrite the content in the non-volatile memory every time a distortion is caused on the image due to a change in the position of the viewpoint. Techniques of Japanese Patent Application Laid-open No. 11-30764 and Japanese Patent Application Laid-open No. 2002-205571 require quite complicated operations for drivers trying to visually recognize an image always in a distortion-free state.